The present invention relates to apparatus and the process for making duplicate image-bearing films from a master film on which intelligence is recorded in the form of relief or deformation images. The way in which intelligence exists on prerecorded photoplastic film is so different from that which is found on more traditional microfiche and microfilm as to render the traditional processes for generating duplicate film unuseable.
In order to simplify the discussion herein, the term "mircofiche" will be used throughout. Those skilled in the art will understand, however, that the discussion applies to microfilm as well as to microfiche.
Although photoplastic film is known (see for example, the structures disclosed in U.S. Pat. Nos. 3,268,361 and 3,592,643) it is still relatively new. One of its principal advantages is that it is updateable, i.e. single microfiche frames can be exposed and developed without affecting other frames and previously recorded frames can be annotated and/or erased and rerecorded. This updateability feature makes photoplastic fiche particularly suitable for use in recording and storing active files. Prior art films, such as silver halide, on the other hand, were, in most instances, restricted to recording dead or substantially inactive files. Recording and storing live files on photoplastic microfiche permits creation of a system whereby the integrity of an organization's files is improved dramatically. A central file area can be established where original documents are immediately recorded on photoplastic microfiche and the hard copy originals permanently stored or destroyed. Thereafter, requests for files are satisfied by supplying duplicates produced on conventional microfiche, which duplicates can be disposed of when no longer needed. The photoplastic masters need never leave the central filing area.
Traditionally, duplicates have been made by projection through lenses or by contact duplication. Duplication through use of an optical system is not preferred, in part, because lenses are expensive and because of the space normally required to accommodate the light path. Additionally, optical systems have proven unsatisfactory in producing acceptable quality duplicates from photoplastic film masters. Contact duplicating from a photoplastic master also yields duplicates of inferior quality. It has been found, however, that one can produce duplicates from such a master by projecting light from the master through a small gap onto the duplicate film. One such method is disclosed in U.S. Pat. No. 3,809,473, although no apparatus is disclosed therein for implementing that process.
The primary criteria in evaluating the quality of microfiche recordings are contrast and resolution. In general, I have discovered that when employing the gap duplicating process described herein, as gap size is increased, although contrast is enhanced, resolution deteriorates. Thus, there is an apparent incompatability between quality duplicating, where both high resolution and high contrast are required, and use of the gap duplicating process.
In the gap duplicating process, at least moderately collimated light is used. I have found, however, that the degree of collimation needed depends upon the gap size. The smaller the gap, the less the requirement for a high degree of collimation. Since collimation reduces the energy available to irradiate the film, for a given required irradiation intensity, the less the light must be collimated, the lower the source luminance that is needed. Conversely, the more the light must be collimated, the lower the irradiance available from a given source.
Since the exposure time required is a function of the intensity of irradiation, the less the collimation that is needed the better. Stated another way, for a predetermined exposure time, as collimation demands increase so too must the intensity of the source.
Thus, as gap size is reduced, resolution improves and the collimation, power and/or exposure times needed are reduced. However, as gap size is reduced, so too is contrast and the ability to duplicate low signal strength intelligence.
"Signal strength" is a parameter which I presently believe is related to the contour of the deformations in the photoplastic film. Normally, it has been my experience that high signal strength intelligence does not duplicate well when a large gap is employed, but low signal strength intelligence is lost when too small a gap is employed.
I have discovered that to accommodate the abovementioned divergent needs of the system, the gap between the emulsion face of the master and the emulsion face of the duplicate must be between about 1 and 3.5 mils. Preferably it should be between about 2.5 and 3.5 mils. To produce acceptable duplicates using a gap within these ranges, I found, the photoplastic master must carry relatively high signal strength intelligence. In order to record, with suitably high signal strength intelligence, from a wide range of originals, it has been discovered that the master fiche must have a relatively thick thermoplastic emulsion layer. Layers less than about 8.mu. thick do not produce recordings with sufficiently high signal strength to be used with suitably small gaps. At the other extreme, the resolution of images recorded on emulsion layers of greater than about 25.mu. is very poor. The optimum emulsion thickness appears to be between 14 and 20.mu..
These comparatively thick emulsions are capable of recording high signal strength images of high contrast and they can be duplicated using gaps within the above-specified range.
The process and apparatus described herein take advantage of these discoveries of the interrelationships between gap size, emulsion thickness, signal strength, contrast and resolution. They are capable of producing high contrast duplicate microfiche with resolution in excess of 200 line pairs per millimeter from a wide variety of hard copy originals, and can do so despite normal line voltage fluctuations and light source deterioration. In addition, duplicates made on the disclosed apparatus have uniformly exposed frames, each of which includes identification of the location or address of the corresponding frame on the master fiche.